Organic optoelectronic devices are becoming widely desirable due to various reasons such as the organic devices are cost effective, the inherent properties of the organic material such as flexibility, fluorescent properties, color tunability using functionalized molecules make them suitable for particular applications.
Designing of luminescent organic material plays a pivotal role in development of optoelectronic devices with improved energy consumption. Research is more focused on providing solid light emitters for their practical applications in optoelectronic devices, such as organic light-emitting diodes. The solid state fluorescent material known in the art are heavily relied on mere functionalization of existing fluorophores. However, considering the demand of solid light emitters in material science and biology, there is an urgent need for the identification of novel core structures, with full colour-tunability, capable of emitting light in the aggregation state.
Organoborons have attracted considerable attention in the scientific fraternity due to their unique electronic structure and interesting optical property derived from the intrinsic pΠ-p* conjugation between the vacant px-orbital of the boron atom and the Π* orbital of the p-conjugated framework.
The most potential examples of fluorescent organoboron compounds are borondipyrromethene (BODIPY) dyes and its analogues which are only emissive in dilute solutions and their fluorescence is quenched severely in the aggregate state [L. Bonardi, H. Kanaan, F. Camerel, P. Jolinat, P. Retailleau, R. Ziessel, Adv. Funct. Mater. 2008, 18, 401]. Hence, a more robust highly emissive solid organoborons are needed.
PCT application WO2011099331, discloses a novel boron-containing compound which is useful as a light-emitting material for organic EL elements or N-type semiconductors; a boron-containing polymer obtained using the compound; and a process for the preparation of the boron-containing compound, which enables low-cost production of the boron-containing compound and the boron-containing polymer. A light-emitting material which contains a boron-containing compound that has a boron atom and a double bond and that has a specific structure. A luminescent material comprising a boron-containing compound having a boron atom and a double bond,
the boron-containing compound represented by the following formula (1);
Article titled “Aggregation-induced emission and efficient solid-state fluorescence from tetraphenylethene-based N,C-chelate four-coordinate organoborons” by Zujin Zhao et al. published in Chemistry European Journal, 2013, 19, 11512-11517 reports boron compounds containing the TPE moiety and N,C-chelate of formula 2 and to the synthesis thereof. Here quantum yield of chelate compounds are 0.40, 0.94 and 0.019.
Article titled “Synthesis of pyridine-borane complexes via electrophilic aromatic borylation” by Naoki Ishida et al. published in Journal of Organic Chemistry, 2010, 75, 8709-8712 reports synthesis of Pyridine-borane complexes from 2-arylpyridines through an electrophilic aromatic borylation reaction with BBr3.
Article titled “From blue to red: syntheses, structures, electronic and electroluminescent properties of tunable luminescent N,N chelate boron complexes” by Q. D. Liu et al. published in Advances Functional Materials, 2005, 15, 1, pp 143-154 reports A comprehensive study of a series four-coordinate boron compounds with the general formula of BPh2(N,N), where N,N are bidentate chelate ligands containing both neutral and negatively charged nitrogen donor atoms has been conducted. The structures of the boron complexes were examined via single-crystal X-ray diffraction.
Article titled “Four-coordinate organoboron compounds with a π-conjugated chelate ligand for optoelectronic applications” by Ying-Li Rao et al. published in Inorganic Chemistry, 2011, 50 (24), pp 12263-12274 reports Four-coordinate organoboron compounds that possess a conjugated chelate ligand have found important applications in advanced materials including emitters and electron-transport materials for organic light-emitting diodes, photochromic materials, and sensing and imaging materials. The recent advances in optoelectronic applications of four-coordinate organoboron compounds are presented in this article.
Article titled “Cooperative catalysis with metal and secondary amine: synthesis of 2-substituted quinolines via addition/cycloisomerization cascade” by Nitin T. Patil et al. published in Journal of Organic Chemistry, 2010, 75 (20), pp 6961-6964 reports a cooperative catalytic system, consisting of CuI and pyrrolidine, has been developed for an efficient synthesis of 2-substituted quinolines. A combination of both the catalysts is necessary; the use of either catalyst alone does not give the product.
Article titled “Photochromic four-coordinate N,C-chelate boron compounds” by Ying-Li Rao et al. published in Coordination Chemistry Reviews, 2012, 256, 5-8, pp 759-770 reports four-coordinate organoboron compounds with a N,C-chelate backbone have been found recently to display an unusual photoisomerization phenomenon with a distinct change of color.
Article titled “Enhancing the photochemical stability of N,C-chelate boryl compounds: C—C bond formation versus C═C bond cis, trans-isomerization.” by Chul Baik et al. published in Journal of American Chemical Society, 2009, 131, 14549-14559 reports N,C-Chelate boron compounds such as B(ppy)Mes2 (ppy=2-phenylpyridyl, Mes=mesityl) have been recently shown to undergo a facile and reversible C—C/C—B bond rearrangement upon irradiation with UV-light, quenching the emission of the sample and limiting their use in optoelectronic devices. It also disclosed Stoke's shift.
Article titled “Steric and electronic influence on photochromic switching of N,C-chelate four-coordinate organoboron compounds” by Hazem Amarne et al. published in Chemistry—A European Journal, 2010, 16(16):4750-61 reports a four-coordinate organoboron compound B(ppy)Mes(2) (1, ppy=2-phenylpyridyl, Mes=mesityl) was previously found to undergo reversible photochromic switching through the formation/breaking of a C—C bond, accompanied by a dramatic color change from colorless to dark blue.
Article titled “N^N- and N^C chelate four-coordinate organoboron compounds: synthesis, properties and applications” by Jiasheng Lu published as thesis 2013 reports the synthesis of N^N- and N^C-chelate four coordinate organoboron compounds and the investigation of their photophysical and photochemical properties.
US Pat. Appl. No. 20120253044 discloses organoboron compounds are described that upon exposure to light, absorb light and isomerize and form a dark-colored isomer. The dark-colored isomer converts back to the colorless isomer upon removal of light, or exposure to oxygen or heat. Such compounds can be added into polymeric matrices such as films.
Inspired by the prior art reports, the present inventors felt a need to provide novel class of N,C-chelate four-coordinate organoborons with different emission colors. The present inventors further observed that with the appropriate choice of the substituents on boron or quinoline, full color tunability can be obtained which can span the whole visible region.